In this section, we present few basic and necessary definitions, for more details one can refer[1]}, [2]}, [3]}, [4]}. A non empty collection of symbols is an alphabet \(\Sigma \) . A sequence of finite or infinite symbols from \(\Sigma \)  forms a word. Length of a word \(w\)  is the number of letters in \(w\) , denoted by \(l(w)\)  and \(\Sigma ^*\)  is the set of all finite words and \(\Sigma ^n\)  is the set of all words over \(\Sigma \)  of length \(n\) . A word \(u\)  is a factor of \(w=w_1w_2\ldots \) , if \(u=w_iw_{i+1}\ldots w_{i+k-1}\) , and is denoted by \(w[i;k]\)  for some \(i,k\in {N}\) . Here, \(w_i\)  denotes the symbol in the \(i\) th position of \(w\) , and \(w[i;k]\)  is the word that starts at position \(i\)  and has length \(k\) . Any factor \(u\)  is a prefix(suffix) of \(w\)  if \(w=ux(w=xu)\) , \(x\in \Sigma ^*\) .
